A typical automatic transmission includes a set of friction clutches that selectively couple rotatable input and output members of the transmission. Engagement of the friction clutches in different combinations connects ring gear, sun gear, and carrier members of one or more planetary gear sets together to achieve a desired transmission output speed ratio. A clutch-to-clutch shift from one transmission output speed ratio to another is performed automatically in response to commands from a controller. A clutch associated with the current speed ratio, i.e., the offgoing clutch, is released, and a clutch associated with a desired new speed ratio is applied, with the newly applied clutch referred to as the oncoming clutch.
When engine torque is positive in a clutch-to-clutch upshift, the oncoming clutch reacts against output torque from the engine. This reaction acts to pull down turbine speed to a level that is more suitable for the commanded gear. However, under some circumstances the direction of engine output torque can become negative, for instance during a regenerative braking event or during certain coasting conditions. An upshift of the transmission commanded during a period of negative engine torque is referred to as a negative torque upshift.